1. Field of the Invention
The present invention generally relates to crystal producing method and apparatus, and particularly relates to a method and apparatus for producing a crystal or thin film by using vapor growth reaction, and particularly to such a method and apparatus, in which a substrate or wafer is induction-heated directly or indirectly by using a high-frequency coil having gas blowout ports arranged so as to face a surface of the substrate in a reaction chamber under the condition of reduced or ordinary pressure and, at the same time, a reactive gas or a raw gas is supplied through the gas blowout ports so as to chemically etch the surface of the substrate or wafer, or so as to precipitate monocrystal, polycrystal or amorphous solids (semiconductors, oxides, nitrides, metals, alloys, or other compounds of silicon).
2. Description of the Related Art
In recent years, semiconductor wafers, especially silicon wafer substrates, have been used popularly for solar cells; discrete semiconductor devices such as transistors, diodes, etc.; ICs (Integrated Circuits), and ULSIs (Ultra Large Scale Integrated Circuits).
A large number of processing techniques are used for producing those devices on substrate wafers. Among the techniques, a CVD (Chemical Vapor Deposition method), etching (chemical etching), and heat-treatment (annealing) method in an inert gas are used as processes using vapor phase reaction. For example, there is used an epitaxial growth (thin-film monocrystal growth) method under ordinary or reduced pressure, formation of various kinds of thin films such as an oxide film, a nitride film, a polycrystal silicon film, a metal thin film, etc., by the CVD method, high-temperature etching using a hydrochloric acid gas, or the like.
With the increase of density and integration of devices and the increase of size (to 12-16".phi.) of substrate crystals, demands on improvement of substrate material quality and accuracy have become severe, so that great reduction of material and equipment cost attended with improvement of accuracy in machining processes and mass-production has become more and more important.
Prior to the description of the present invention, a silicon epitaxial growth apparatus will be described as an example of the process of this type.
FIG. 22 is a view showing a conventional producing apparatus for vertical silicon epitaxial crystal growth using high-frequency heating. Referring to FIG. 22, the process of crystal growth will be described below. In FIG. 22, the reference numeral 1 designates a high-frequency coil; 5, a raw gas introduction pipe; 7, gas diffusion holes provided at an end of the introduction pipe 5; 8, a silicon monocrystal substrate; 9, a carbon susceptor having a shape like a doughnut type disk; 11, a carbon susceptor support; 33, a bell jar to form a reaction chamber; 34, an exhaust gas outlet; and 35, a coil cover made of quartz.
In FIG. 22, the silicon substrate 8 is arranged on the carbon susceptor 9 and heated indirectly by heat conduction through the carbon susceptor 9 heated by the high-frequency coil 1. The heating temperature is generally in a range of from 900.degree. C. to 1200.degree. C. The carbon susceptor 9 is arranged on the support 11 and rotated to make the temperature distribution uniform. In this state, a raw gas is introduced, through the raw gas introduction pipe 5 in the center, into a container which is constituted by the bell jar 33 to form a reaction chamber. The raw gas is then blown out from the gas diffusion holes 7. Examples of the raw gas are monosilane (SiH.sub.4 /H.sub.2), dichlorsilane (SiH.sub.2 Cl.sub.2 /H.sub.2), trichlorsilane (SiHCl.sub.3 /H.sub.2), tetrachlorsilane (SiCl.sub.4 /H.sub.2), etc. Hydrogen is used as a transport gas.
The raw gas blown out through the gas diffusion holes 7 partly reaches the surface of the heated silicon substrate 8 and is subjected to heat decomposition or reducing reaction, so that silicon is precipitated and epitaxially grown as a monocrystal on the surface of the substrate. In this occasion, impurities (P type: B.sub.2 Cl.sub.4, N type: PH.sub.2, AsH.sub.3) are supplied to the raw gas so that resistivity in the growth layer is adjusted. Although part of the raw gas is precipitated on the surface of the substrate, other raw materials are precipitated on the susceptor 9 and on the wall of the container and the residual part of the raw gas as an unreacted part is ejected out of the container through the exhaust gas outlet 34.
Although FIG. 22 shows the case where a method using high-frequency induction heating is used as the method of heating the substrate 8, there may be used a heating method using a resistor as a heating source, a heating method using an infrared lamp as a heating source, and so on.
In the epitaxial growth method according to the aforementioned prior art, not only the loss of electric power is large because a large-scale susceptor having a volume several hundred times as large as the volume of the wafers which are silicon substrates is heated, but also the utilization rate of the raw gas to be used effectively as an epitaxial layer on the wafers is very low because the raw gas supplied is circulated in the apparatus. The utilization rate is only several percents by weight of a raw material. Most of component gases are polycrystallized and precipitated on the substrate support (susceptor) and on the wall of the container or ejected out of a system as unreacted gases.
Furthermore, in the aforementioned prior art, the growth speed of the epitaxial growth layer depends on a diffusion rate determining layer in the surface of the wafers, so that, generally, the growth speed is in a range of from about 0.5 .mu.m/min to about 3 to about 3 .mu.m/min and cannot be selected to be so higher. In addition, the impurities (boron, arsenic, phosphorus, antimony, etc.) added into the substrate wafer are gasified so as go round from the rear surface to the front surface, so that the impurities are incorporated into the epitaxial growth layer again. As a result, auto-doping occurs to make it difficult to control the distribution of impurities between the epitaxial layer of the epitaxial wafer and the substrate wafer and the resistivity in the epitaxial layer.
In the high-frequency heating method or in the resistance heating method, the gradient of heat in the wafers is large so that distortion due to heat stress easily causes sliding or slipping (crystal defects) of crystal faces in the crystal of the wafers, because the heat of the susceptor is transmitted to the wafers by heat conduction. Furthermore, because the size of the susceptor is large so that the heat capacity is large, a large time is required for changing the temperature to thereby cause lowering of throughput (the number of times of growth per time). Furthermore, not only the size of the apparatus is made large but also the susceptor and the quartz-containing bell jar are made expensive.
In the infrared lamp heating method, distortion due to the gradient of heat in the wafers is small so that slipping little occurs, because the wafers are directly heated. The method, however, has disadvantages in the short life (large consumption) of the lamp and the complex structure of the lamp house. In addition, the method has disadvantages in the large loss of electric power because of the necessity of heating the large-scale cylinder type susceptor, the complex maintenance of the apparatus, and so on.
On the other hand, the diameter of the wafers has been increased greater and greater. The diameter which was conventionally in a range of from 150 mm to 200 mm has a tendency to increase so that wafers having a diameter in a range of from 300 mm to 400 mm will be made the main current in the future. Accordingly, a sheet type apparatus has been made the main current because the size becomes large in the conventional batch type apparatus.